The long-term objective of this research is to study the mechanisms by which the activities of lipogenic enzymes are regulated and the effects of nutrition on these mechanisms. The specific aims are: 1) to determine the extent to which nutritional variables such as the state of biotin and pantothenic acid nutrition, dietary mercury and fat levels, length of starvation or length of refeeding following starvation affect the absolute activities of the lipogenic enzymes acetyl-CoA carboxylase (ACC) and fatty acid synthetase (FAS), and 2) to correlate changes in absolute activities of the lipogenic enzymes brought about by nutritional means with observed changes in lipogenesis rate in intact animals. Implicit in these aims is a determination of whether ACC or FAS is the rate-limiting enzyme for lipogenesis and whether the same enzyme is rate-limiting under all nutritional and physiological conditions. The methodcological approach will be to measure the absolute amounts of enzymes in terms of IN VITRO activity and purification and/or immunoprecipitation of enzyme and to change the absolute amounts or activities by imposing nutritional variables. IN VIVO lipogenesis will be measured in the same animals. The rate-limiting lipogenic enzyme presumably will be that enzyme whose absolute activity correlates most closely with IN VIVO lipogenesis rate.